Etymology[change | change source]
Thou comes from the Germanic Languages, a shortening of thousandth.
Mil comes from the Latin Languages, a shortening of mille.
History[change | change source]
The thou was introduced in 1844 by Joseph Whitworth as a substitute to traditional fractions such as 1⁄64 1⁄32 1⁄16 1⁄8 which cannot be defined simply in hundredths unlike 1⁄4 (0.25) or 1⁄2 (0.5). Traditional fractions continued to be used, as they were a substantial part of other units of length.
Length[change | change source]